This invention relates generally to integrated optical circuits and the components making up such circuits, and, more particularly, to an integrated optical switch made completely of silicon and whose index of refraction is controlled by an external light-beam shining on the switch.
With recent increased development of lasers and optical fibers, more attention has been directed to integrated optical systems or circuits and the components which make up these circuits. Particular concern has been directed to the area of optical communciations which operate at a wavelength 1.3 .mu.m and beyond and the integrated optical circuits which are utilized therein. Since it has been recognized that integrated optical components are capable of coupling efficiently to single-mode optical fibers, such integrated optical components become essential parts of fiber optic communication networks devoted to telecommunications or data communications applications. An excellent example of one such integrated component is the integrated optical switch which finds great utility in its ability to switch in a selected user at each local terminal of, for example, a local-area network.
As pointed out above, of major concern is the transmission of electromagnetic radiation (light) at the 1.3 .mu.m to 1.55 .mu.m wavelength area, the wavelengths at which propagation loss through an optical fiber is at a minimum. Switches are an essential component of such integrated optical circuits since it is required within the circuits to switch light energy from one guided-wave path to another.
Initially, mechanical switches which utilize deflecting mirrors positioned to intercept and redirect the light energy of a beam were utilized. These mechanical switches were replaced by more suitable optical components since speed of switching became an essential criteria in the building of optical communication circuit-networks.
Thereafter, integrated optical components became the preferred switching device. These switches followed two approaches:
(1) the formation of heterostructures using exotic alloys of InP on InP, and
(2) LiNbO.sub.3 components formed by titanium-ion in-diffusion or by proton exchange.
Examples of integrated optical components in InGaAsP/InP can be found in a paper by Mikami et al, "Waveguided Optical Switch In InGaAs/InP Using Free-Carrier Plasma Dispersion", Electronic Letters, Vol. 20, No. 6, Mar. 15, 1984, pp. 228 and 229, while examples of optical components utilizing Ti:LiNbO.sub.3 can be found in a paper by A. Neyer, "Electro Optic X-Switch Using Single Mode Ti:LiNbO.sub.3 Channel Waveguides", Electronics Letters, Vol. 19, No. 14, July 7, 1983, pp. 553 and 554.
There are many drawbacks associated with the formation of heterostructures using exotic alloys of InP on InP. For example, the alloy composition of InGaAsP must be chosen very carefully so that the lattice constant of the quaternary exactly matches the lattice constant of the host InP substrate: the growth apparatus and the growth techniques required to form the alloys are extremely complicated and may include such complex techniques as metal-organic chemical vapor deposition and molecular beam epitaxy; and it is necessary to grow sequentially alternating layers of different materials in order to form the multi-layer heterostructures that are essential in the above-mentioned devices.
The disadvantages with respect to the Ti:LiNbO.sub.3 are also numerous. For example, it is difficult to control the diffusion depth and ionic concentration of the Ti ions; the waveguide profiles are semicircular, which is not at an optimum match to the circular fiber-core profile; and there are a number of stability problems associated with this material.
It is therefore clearly evident that there exists a need for improved optical switches, and in particular, it would be highly desireable to fabricate an integrated optical component which is not subject to the drawbacks associated with prior art optical components.